Raman microscopy is a useful spectroscopic technique that permits nondestructive, spatially resolved measurements within the samples. Conventional Raman microscopes such as those disclosed in U.S. Pat. No. 5,194,912 to Batchelder et al. suffer from bulky sizes, which limits them only to laboratory usages. Recently, with the development of diode lasers as the excitation light source, Raman spectrometers were made as compact attachments that can be mounted onto a standard microscope to convert it into a Raman microscope. Some exemplary apparatus can be found in U.S. Pat. No. 7,102,746 to Zhao and U.S. Pat. No. 7,403,281 to Carron et al., which are hereby incorporated herein as references. Yet the large number of optical components in a Raman spectrometer still places a lower limit on its physical size. As a result, the incorporation of the Raman spectrometer inevitably alters the optical path length of the microscope. Certain modifications have to be made to the microscope to accommodate the Raman spectrometer, which may disturb the microscope's originally designed functions.
There thus exists a need for an improved spectroscopic accessory that can be mounted onto a standard microscope to add a spectroscopic function to the microscope and in the meantime induces minimum alteration to the optical path of the microscope.